Track gauge

In rail transport, track gauge (in American English, alternatively track gage) is the distance between the two rails of a railway track. All vehicles on a rail network must have wheelsets that are compatible with the track gauge. Since many different track gauges exist worldwide, gauge differences often present a barrier to wider operation on railway networks. The term derives from the metal bar, or gauge, that is used to ensure the distance between the rails is correct. Railways also deploy two other gauges to ensure compliance with a required standard. A loading gauge is a two-dimensional profile that encompasses a cross-section of the track, a rail vehicle and a maximum-sized load: all rail vehicles and their loads must be contained in the corresponding envelope. A structure gauge specifies the outline into which structures (bridges, platforms, lineside equipment etc.) must not encroach. The most common use of the term "track gauge" refers to the transverse distance between the inside surfaces of the two load-bearing rails of a railway track, usually measured at to below the top of the rail head in order to clear worn corners and allow for rail heads having sloping sides. The term derives from the "gauge", a metal bar with a precisely positioned lug at each end that track crews use to ensure the actual distance between the rails lies within tolerances of a prescribed standard: on curves, for example, the spacing is wider than normal. Deriving from the name of the bar, the distance between these rails is also referred to as the track gauge. Permanent way (history)Wagonway and Plateway The earliest form of railway was a wooden wagonway, along which single wagons were manhandled, almost always in or from a mine or quarry. Initially the wagons were guided by human muscle power; subsequently by various mechanical methods. Timber rails wore rapidly: later, flat cast-iron plates were provided to limit the wear. In some localities, the plates were made L-shaped, with the vertical part of the L guiding the wheels; this is generally referred to as a "plateway".